Gas turbines typically produce high temperatures and heavy vibrations during operation, and these conditions can be damaging to many materials used in the construction of the turbines. Consequently, the types of materials that can be used is quite limited. For example, suitable materials must have high-strength and low-weight characteristics while at the same time be able to withstand high temperatures. Engineers have considered certain metal alloys, composites and ceramics among the materials to be used in such an environment.
Ceramics have been considered because of their comparatively light weight and high melting points. Unfortunately, ceramics can be relatively brittle, especially when used as structural components. Despite this shortcoming, design considerations may nevertheless dictate the incorporation of ceramics in certain structural applications, such as in the construction of fan or turbine blade assemblies in a turbine engine.
When fastening ceramic materials to other structures, great care must be taken because these ceramic materials may be intolerant to local stresses introduced by a fastener. These stresses can arise, for example, from fixed displacement of the fastener due to the vibrational forces generated from the operation of the turbine.
Thermal stresses may also be present when ceramics interface with fasteners or other structures made of dissimilar materials, especially those having different coefficients of thermal expansion. In comparison to metals, ceramics have a relatively low coefficient of thermal expansion. Thus, when a metal fastener, such as a metal bolt, disposed in an opening of a ceramic structure is heated, the bolt will expand radially more than the surrounding ceramic. Eventually, the metal fastener may come into contact with the surrounding ceramic, applying potentially cracking forces.
Therefore, there is a continuing need for a system for fastening dissimilar materials, such as metals and ceramics, that is capable of distributing vibrationally and thermally induced loads while avoiding local high strain conditions. Moreover, there is a need for such a fastening system that permits easy removal when necessary.